Many types of heavy crude oils contain high concentrations of sulfur compounds, organo-metallic compounds, and heavy non-distillable fractions called asphaltenes that are insoluble in light paraffins such as n-pentane. Because most petroleum products used for fuel must have a low sulfur content, the sulfur compounds in the non-distillible fractions reduce their value to petroleum refiners and increase their cost to users of such fractions as fuel or as raw material for producing other products. In order to increase the saleability of these non-distillable fractions, refiners must resort to various expedients for removing sulfur compounds.
A conventional approach to removing sulfur compounds in distillable fractions of crude oil, or its derivatives, is catalytic hydrogenation in the presence of molecular hydrogen at moderate pressure and temperature. While this approach is cost effective in removing sulfur from distillable oils, problems arise when the feed includes metallic containing asphaltenes. Specifically, the presence of metallic containing asphaltenes results in catalyst deactivation by reason of the coking tendency of the asphaltenes, and the accumulation of metals on the catalyst, especially nickel and vanadium compounds commonly found in the asphaltenes.
Alternative approaches include coking, high-pressure, desulfurization and fluidized catalytic cracking of non-distillable oils, and production of asphalt for paving and other uses. All of these processes, however, have disadvantages that are intensified by the presence of high concentrations of metals, sulfur and asphaltenes. In the case of coking non-distillable oils, the cost is high and a disposal market for the resulting high sulfur coke must be found. Furthermore, the products produced from the asphaltene portion of the feed to a coker are almost entirely low valued coke and cracked gases. In the case of residual oil desulfurization, the cost of high pressure equipment, catalyst consumption, and long processing times make this alternative undesirably expensive.
In U.S. Pat. No. 4,191,636, heavy oil is continuously converted into asphaltenes and metal-free oil by hydrotreating the heavy oil to crack asphaltenes selectively and remove heavy metals such as nickel and vanadium simultaneously. The liquid products are separated into a light fraction of an asphaltene-free and metal-free oil and a heavy fraction of an asphaltene and heavy metal-containing oil. The light fraction is recovered as a product and the heavy fraction is recycled to the hydrotreating step.
In U.S. Pat. No. 4,528,100, a process for the treatment of residual oil is disclosed, the process comprising the steps of treating the residual oil so as to produce a first extract and a first raffinate using supercritical solvent extraction, and then treating the first raffinate so as to produce a second extract and a second raffinate again by second raffinate again by supercritical solvent extraction using a second supercritical solvent and then combining the first extract and the raffinate to a product fuel. In accordance with a particular embodiment of the invention disclosed in the U.S. '100 patent, the supercritical solvents are particularly selected to concentrate vandium in the second extract. Thus, even though the amount of vandium present in the produce fuel is low and consequently beneficial for reducing gas turbine maintenance problems as stated in this '100 patent, some amount of vanadium does still remain therein.
Another example of a user of the heavier, higher boiling range portion of a hydrocarbon is a refinery with a fluid catalytic cracking unit (a FCC unit). FCC units typically are operated with a feedstock quality constraint of very low metals asphaltenes, and CCR (i.e., less than 10 wppm metals, less than 0.2 wt % asphaltenes, and less than 2 wt % CCR). Utilization of feedstocks with greater levels of asphaltenes of CCR results in increased coke production and a corresponding reduction in unit capacity. In addition, use of feedstocks with high levels of metals and asphaltenes results in more rapid deactivation of the catalyst, and thus increased catalyst rates and increased catalyst replacement costs.
In U.S. Pat. No. 5,192,421, a process for the treatment of whole crude oil is disclosed, the process comprising the steps of deasphalting the crude by first mixing the crude with an aromatic solvent, and then mixing the crude-aromatic solvent mixture with an aliphatic solvent. The U.S. '421 patent (at page 9, lines 43-45) identifies that certain modifications must be made to prior art solvent deasphalting technologies, such as that described in U.S. Pat. Nos. 2,940,920, 3,005,769, and 3,053,751 in order to accommodate the process described in the U.S. '421 patent, in particular since the prior art solvent deasphalting technologies have no means to remove that portion of the charge oil that will vaporize concurrently with the solvent and thus contaminate the solvent used in the process. In addition to being burdened by the complexity and cost resulting from the use of two solvents, the U.S. '421 process results in a deasphalted product that still contains a non-distilled portion with levels of CCR and metals that exceed the desired levels of such contaminants.
In U.S. Pat. No. 4,686,028 a process for the treatment of whole crude oil is disclosed, the process comprising the steps of deasphalting a high boiling range hydrocarbon in a two-stage deasphalting process to separate asphaltene, resin, and deasphalted fractions by hydrogenation or visbreaking. The U.S. '028 patent is burdened by the complexity and cost of a two-stage solvent deasphalting system used to separate the resin fraction from the deasphalting oil. In addition, like the U.S. '421 patent, the '028 process results in an upgraded product that still contains a non-distilled fraction—the DAO—that is contaminated with CCR and metals.
Metals contained in heavy oils contaminate and spoil the performance of catalysts in fluidized catalytic cracking units. Asphaltenes present in such oils are converted to high yields of coke and gas which burden an operator with high burning requirements.
Another alternative available to a refiner or heavy crude user is to dispose of the non-distillable heavy oil fractions as fuel for industrial power generation or as bunker fuel for ships. Disposal of such fractions as fuel is not particularly profitable to a refiner because more valuable distillate oils must be added in order to reduce viscosity sufficiently (e.g. producing heavy fuel oil, etc.) to allow handling and shipping. Furthermore, the presence of high sulfur and metals contaminants lessens the value to the users. In addition, this does not solve the problem of the non-distillable heavy oil fractions in a global sense since environmental regulations restrict the use of high sulfur fuel oil. Refiners frequently use a thermal conversion process, e.g., visbreaking, for reducing the heavy fuel oil yield. This process converts a limited amount of the heavy oil to lower viscosity light oil, but has the disadvantage of using some of the higher value distillate oils to reduce the viscosity of the heavy oil sufficiently to allow handling and shipping. Moreover, the asphaltene content of the heavy oil restricts severely the degree of visbreaking conversion possible due to the tendency of the asphaltenes to condense into heavier materiels, even coke, and cause instability in the resulting fuel oil. Furthermore, this process reduces the amount of heavy fuel oil that the refiner has to sell and is not useful in a refinery processing heavy crudes.
Many proposals thus have been for dealing with crude oil and metals. And while many are technically viable, they appear to have achieved little or no commercialization, due, in large measure, to the high cost of the technology involved. Usually such cost takes the form of increased catalyst contamination by the metals and/or the carbon deposition resulting from the attempted conversion of the asphaltene fractions.
An example of the processes proposed in order to cope with high metals and asphaltenes is disclosed in U.S. Pat. No. 4,500,416. In one embodiment, an asphaltene-containing hydrocarbon feed is solvent deasphalted in a deasphalting zone to produce a deasphalted oil (DAO) fraction, and an asphaltene fraction which is catalytically hydrotreated in a hydrotreating zone to produce a reduced asphaltene stream that is fractionated to produce light distillate fractions and a first heavy distillate fraction. Both the first heavy distillate fraction and the DAO fraction are thermally cracked into a product stream that is then fractionated into light distillate fractions and a second distillate fraction which is routed to the hydrotreating zone.
In an alternative embodiment, an asphaltene-containing hydrocarbon feed is solvent deasphalted in a deasphalting zone to produce a deasphalted oil (DAO) fraction, and an asphaltene fraction which is catalytically hydrotreated in a hydrotreating zone to produce a reduced asphaltene stream that is fractionated to produce light distillate fractions and a first heavy distillate fraction. The first heavy distillate fraction is routed to the deasphalting zone for deasphalting, and the DAO fraction is thermally cracked into a product stream that is then fractionated into light fractions and a second heavy distillate fraction which is routed to the hydrotreating zone.
In each embodiment in the '416 patent, asphaltenes are routed to a hydrotreating zone wherein heavy metals present in the asphaltenes cause a number of problems. Primarily, the presence of the heavy metals in the hydrotreater causes deactivation of the catalyst that increases the cost of the operation. In addition, such heavy metals also result in having to employ higher pressures in the hydrotreater which complicates its design and operation and hence its cost.
It is therefore an object of the present invention to provide a new and improved method of and apparatus for processing and upgrading heavy hydrocarbon feeds containing sulfur, metals, and asphaltenes, wherein the disadvantages as outlined are reduced or substantially overcome.